Vacancy-induced magnetism of beryllium monoxide

The electronic and magnetic states of beryllium monoxide BeO with lattice vacancies were investigated by the PAW-VASP ab initio band structure method. In the presence of defects in the beryllium sublattice, vacancy-induced magnetic moments arise on the oxygen atoms, and the nonstoichiometric Be_1?x O passes to the magnetic half-metal state.     

Synthetic, reactivity, and structural studies on half-sandwich (eta5-C5Me5)Be and related compounds: halide, alkyl, and iminoacyl derivatives

The half-sandwich compounds [(eta(5)-C(5)Me(5))BeX] (X=Cl, 1 a; Br, 1 b), readily prepared from the reaction of the halides BeX(2) and M[C(5)Me(5)] (M=Na or K), are useful synthons for other (eta(5)-C(5)Me(5))Be organometallic compounds, including the alkyl derivatives [(eta(5)-C(5)Me(5))BeR] (R=Me, 2 a; CMe(3), 2 b; CH(2)CMe(3), 2 c; CH(2)Ph, 2 d). The latter compounds can be obtained by metathetical exchange of the halides 1 with the corresponding lithium reagent and exhibit NMR signals and other properties in accord with the proposed formulation. Attempts to make [(eta(5)-C(5)Me(5))BeH] have proved fruitless, probably due to instability of the hydride toward disproportionation into [Be(C(5)Me(5))(2)] and BeH(2). The half-sandwich iminoacyl [(eta(5)-C(5)Me(5))Be(C(NXyl)Cp')] and [(eta(5)-C(5)Me(4)H)Be(C(NXyl)Cp')]3, 6 where Xyl=C(6)H(3)-2,6-Me(2) and Cp'=C(5)Me(5) or C(5)Me(4)H, are formed when the beryllocenes [Be(C(5)Me(5))(2)], [Be(C(5)Me(4)H)(2)], and [Be(C(5)Me(5))(C(5)Me(4)H)] are allowed to react with CNXyl. Isolation of three different iminoacyl isomers from the reaction of the mixed-ring beryllocene [(eta(5)-C(5)Me(5))Be(eta(1)-C(5)Me(4)H)] and CNXyl, namely compounds 5 a, 5 b, and 6, provides compelling evidence for the existence in solution of different beryllocene isomers, generated in the course of two very facile processes that explain the solution dynamics of these metallocenes, that is the 1,5-sigmatropic shift of the Be(eta(5)-Cp') unit around the periphery of the eta(1)-Cp' ring, and the molecular inversion rearrangement that exchanges the roles of the two rings.     

Microcalorimetric Evaluation of Precipitation in Cu–2Be–0.2Mg

Beryllium precipitation from the Cu-rich matrix in a Cu–2 mass% Be–0.2 mass% Mg alloy homogenized and quenched from 1073 K was studied by differential scanning calorimetry (DSC). The DSC traces showed two main exothermic effects, A and B, each comprising two subeffects: A₁ and A₂ , and B₁ and B₂ respectively. Effects A₁ and A₂ correspond to the precipitation of GP zones and subsequent overlapping and independent precipitation of the phase. Only at very low heating rates can be inherited from GP zones. Effects B₁ and B₂ correspond to heat evolved during transitions to the states with and phases, respectively. Heat effect A can be quantitatively described in terms of solid solubilities before and after precipitation, and of the precipitation heats of the phases involved. The heat content of the combined GP zone/ phase precipitation effect was proportional to the number of beryllium atoms precipitated, yielding an average value of 21 kJ mol^–1 beryllium for beryllium precipitation. It was shown that the phase arises from the combined transition from states with GP zones and phases, whereas arises from the transition of states with and phases. The apparent activation energies associated with GP zones and , and phases are 1.16±0.08, 1.18±0.07, 1.37±0.08 and 1.74±0.09 eV, respectively. These values are discussed in terms of the mobility of dissolved atoms related to the concentrations of excess vacancies and solute-vacancy complexes, and the direction of plate-like precipitate growth (either normal or perpendicular to the plate). It is inferred that the main roles of magnesium are to decrease the amount and rate of GP formation, to enhance the volume fraction of and to suppress the discontinuous precipitation of .This revised version was published online in November 2005 with corrections to the Cover Date.     

Carbon Monoxide Bonding With BeO and BeCO3: Surprisingly High CO Stretching Frequency of OCBeCO3

The complexes OCBeCO₃ and COBeCO₃ have been isolated in a low‐temperature neon matrix. The more stable isomer OCBeCO₃ has a very high C? O stretching mode of 2263 cm^?1, which is blue‐shifted by 122 cm^?1 with respect to free CO and 79 cm^?1 higher than in OCBeO. Bonding analysis of the complexes shows that OCBeO has a stronger OC? BeY bond than OCBeCO₃ because it encounters stronger π backdonation. The isomers COBeCO₃ and COBeO exhibit red‐shifted C? O stretching modes with respect to free CO. The inverse change of C? O stretching frequency in OC? BeY and CO? BeY is explained with the reversed polarization of the σ and π bonds in CO.     

Exergonic and Spontaneous Production of Radicals through Beryllium Bonds

High‐level ab initio calculations show that the formation of radicals, by the homolytic bond fission of Y?R (Y=F, OH, NH₂; R=CH₃, NH₂, OH, F, SiH₃, PH₂, SH, Cl, NO) bonds is dramatically favored by the association of the molecule with BeX₂ (X=H and Cl) derivatives. This finding is a consequence of two concomitant effects, the significant activation of the Y?R bond after the formation of the beryllium bond, and the huge stabilization of the F^. (OH^., NH₂^.) radical upon BeX₂ attachment. In those cases where R is an electronegative group, the formation of the radicals is not only exergonic, but spontaneous.     

The Oxygen‐Rich Beryllium Oxides BeO4 and BeO6

Two novel isomers of BeO₄ with the structures OBeOOO and OBe(O₃) in the electronic triplet state have been prepared as well as the known disuperoxide complex Be(O₂)₂ in solid noble‐gas matrices. We also report the synthesis of the oxygen‐rich bis(ozonide) complex Be(O₃)₂ in the triplet state which has a D_2d equilibrium geometry. The molecular structures were identified by infrared absorption spectroscopy with isotopic substitutions as well as quantum chemical calculations.     

Ultrashort Beryllium−Beryllium Distances Rivalling Those of Metal−Metal Quintuple Bonds Between Transition Metals

Chemical bonding is at the heart of chemistry. Recent work on high bond orders between homonuclear transition metal atoms has led to ultrashort metal?metal (TM?TM) distances defined as d_M?M<1.900 Å. The present work is a computational design and characterization of novel main group species containing ultrashort metal?metal distances (1.728–1.866 Å) between two beryllium atoms in different molecular environments, including a rhombic Be₂X₂ (X=C, N) core, a vertical Be?Be axis in a 3D molecular star, and a horizontal Be?Be axis supported by N‐heterocyclic carbene (NHC) ligands. The ultrashort Be?Be distances are achieved by affixing bridging atoms to attract the beryllium atoms electrostatically or covalently. Among these species are five global minima and one chemically viable diberyllium complex, which provide potential targets for experimental realization.     

Beryllium bonding with noble gas atoms

Quantum chemical calculations were carried out to investigate the nature of the bonding between a neutral Be₃ ring and noble gas atom. Electronic structure calculation for these complexes was carried out at different computational levels in association with natural bond orbital, quantum theory of atoms in molecules, electron localization function, symmetry adapted perturbation theory, and molecular electrostatic potential surface analysis of Be₃ complexes. The Be atoms in the Be₃ moiety are chemically bonded to one another, with the Be Be bond dissociation energy being ~125 kJ mol⁻¹. The Be₃ ring interacts with the noble gases through non-covalent interactions. The binding energies of the noble gas atoms with the Be₃ ring increases with increase in their atomic number. The non-covalent interaction index, density overlap region indicator and independent gradient model analyses reveal the presence of non-covalent inter-fragment interactions in the complexes. Energy decomposition analysis reveals that dispersion plays the major role towards stabilizing these systems.     

静电陀螺转子用铍材的基本要求

通过对静电陀螺仪空心转子的功能特性分析，确认铍材是用作空心转子材料的唯一选择。通过对目前国内外铍材的现状的分析，提出空心转子用铍材的主要技术要求，该要求也适用于实心小球铍材。